High-resolution diffraction using Larmor precession and multiple narrow beams defined by multislits

Abstract

A new method is introduced to measure lattice constants by diffraction in Bragg scattering with very high accuracy. Use is made of Larmor precession of a polarized neutron beam in a magnetic field. The number of precessions is directly related to the wavelength of the neutron beam and the phase change in one precession period can be identified as a slightly changed wavelength, which itself is indicative of a change in the lattice parameter. Using multislits as diaphragms in the incident and in the diffracted beams, one selects angular regions of the neutron beam in the scattering plane with phase angles in Larmor precession that differ only by multiples of 2π at a certain magnetic field in the Larmor coil. Doing this, a very high resolution in lattice parameter can be obtained with an intensity, which is a multiple of the intensity in conventional diffraction methods at this high angular resolution. Use of the proposed method in materials science applications such as stresses in materials and in crystal size determination in materials is discussed.